Their work has focused on the steady decline of big cats across the globe. The most recent documentary premiers Dec. 1 at 10 p.m. ET/PT on the cable channel NatGeo Wild.Game of Lions tells the story of a group of young males and the dangers they face as they seek to become the one battle-scarred warrior who will lead the pride. It's part of NatGeo's popular Big Cat Week.

The Jouberts have been National Geographic Explorers-in-Residence since 1999. They worry that a rising hunger in China for lion bone wine and exotic animal pelts is adding to the dangers faced by lions.

Africa's lion population is already down to 20,000 to 30,000, from as many as a million originally, says Luke Hunter, president of Panthera, a global wild cat conservation organization based in New York.

The main current threat is simply more mouths to feed, Hunter said. Africa has the fastest-growing population on the planet, fueling the need to clear more land for farming, destroying the habitat lions need to survive.

But other dangers loom. For centuries tiger bone wine, made by soaking tiger bones in spirits, has been sold in China and across Asia as an elixir believed to have healing powers and as a male potency enhancer.

Today "lion bones have started to replace tiger bones because tigers are being driven to extinction in the wild," says Richard Carroll with the World Wildlife Fund's Africa program.

Two lion cubs tussling in the Okavango Delta in Botswana.(Photo: Beverly Joubert)

The bones come mainly from South African lion farms, where the animals are bred to be hunted, said Tico McNutt, director of the Botswana Predator Conservation Trust in Maun, Botswana.

The concern is that bones from wild lions are beginning to enter China and Chinese markets in Asia. "Once you have any legal trade, it opens up a whole illegal trade," Carroll says.

The Jouberts say they aren't singling out China. "There's no one reason why we're losing the animals in Africa, there are many reasons. We can't target one culture," says Beverly, 56.

At the same time, having spent the last 32 years working to change perceptions abut wildlife, they feel the need to reach beyond their current audience. "Our long Western documentaries don't work in China," where young people prefer short videos on cellphones, Beverly says.

The couple have signed on with a Hong Kong film production group to find cultural intermediaries who can help them translate their award-winning stories into a message that will resonate with the world's most populous nation - while not forgetting their American and European audiences.

Their stories about individual animals "stir emotions and fertilize empathy in ways that science and scientific understanding" cannot, McNutt said.

They certainly look the part to tell those stories. Meeting the Jouberts on a tiny airstrip in Botswana feels like stepping into a Ralph Lauren safari ad. They're all bronzed skin, khaki clothes and savanna hats. Except that they are the real thing - having lived in the African bush since 1977.

"We both felt we'd been born into the wrong era," Beverly says. When Dereck finished his mandatory military service they left Johannesburg to spend a year at a wildlife observation post in South Africa. "We wanted to be explorers. It was almost like a gap year," she said, comparing it to the year between high school and college many Europeans take to travel.

That search for "the real Africa" turned the newly married couple into first researchers, then documentary filmmakers and now conservationists who have the ear of many powerful politicians in southern Africa.

They spend a year or two on each movie, practically living in their SUV. They come to know the animals whose lives they record intimately, spending months around them until they become just another part of the landscape to wildlife.

"Sometimes we just climb up on the roof and sleep there so we don't lose them at dawn," Beverly says.

The one they've just finished, Game of Lions, focuses on males. While male and females cubs are born in equal numbers, by adulthood only one in seven males survives, Dereck says.

Of the cubs they began to follow, only a pair of brothers are still with the pride. "It's those two over there," he says, pointing to them sleeping under a bush in the midday heat.

The film features harrowing moments. One shows the struggles of a tiny male cub being toyed with by a group of adults while his mother is away hunting.

But they can, and do, interfere in the dangers humans pose to lions. They are a powerful force for conservation not only through their movies but also politically in Africa, said Rudi van Aarde, chair of conservation ecology at the University of Pretoria in South Africa.

A male lions leaps across a stream in Botswana's Okavango Delta.(Photo: Beverly Joubert)

"That's because they come across not as activists, but as Africans," van Aarde said. Both are now Botswanan citizens

China's growing middle class is their next objective.

Lion bone wine and other wildlife items "are illegal and rare and desired so they're being consumed as status symbols," Panthera's Hunter said.

However, "really good educational campaigns in China can change things," says Carroll. In recent years, shark fin soup has begun to fall out of favor as Chinese celebrities such as actor Jackie Chan and basketball player Yao Ming speak out against the traditional Chinese delicacy. Conservationists decry it because as many as 10 million sharks a year are slaughtered annually just for their fins.

Stopping the market in lion parts in Asia before it really gets going is an important part of protecting them from the numerous threats they face today and in the future, Beverly says.

It's a smart move, Hunter says. "If they're able to bring that expertise to bear and move the needle even a small amount, it's helpful."

The alpha male of the Duba Plains pride and one of his two sons.(Photo: Elizabeth Weise)